Ion implantation is a process of introducing dopants or impurities into a substrate via bombardment. In semiconductor manufacturing, the dopants are introduced to alter electrical, optical, or mechanical properties. For example, dopants may be introduced into an intrinsic semiconductor substrate to alter the type and level of conductivity of the substrate. In manufacturing an integrated circuit (IC), a precise doping profile provides improved IC performance. To achieve a particular doping profile, one or more dopants may be implanted in the form of ions in various doses and various energy levels.
The beam line components of an ion implanter may include a series of electrodes configured to extract ions from the source chamber, a mass analyzer configured with a particular magnetic field where just ions having a desired mass-to-charge ratio are allowed to pass through the analyzer, and a corrector magnet configured to provide a ribbon beam directed to the platen almost orthogonally with respect to the ion beam to implant the ions into a target substrate. The ions lose energy when the ions collide with nuclei and electrons in the substrate and come to rest at a desired depth within the substrate based on the acceleration energy. The depth of implantation into the substrate is a function of ion energy and the mass of the ions generated in the source chamber. In some approaches, arsenic or phosphorus may be doped to form n-type regions in a substrate, and boron, gallium, or indium may be doped to create p-type regions in a substrate.
Various types of ion sources may be employed for ionizing feed gases. Such sources may be selected based on the type of plasma intended as well as an associated ion beam profile for implantation into a target substrate. One type of ion source is a hot-cathode ion source utilizing an indirectly heated cathode (IHC) to ionize a feed gas in a source chamber. Another type of ion source is an inductively-coupled, RF (radio frequency) plasma ion source utilizing an RF coil to excite, through electromagnetic induction, a feed gas in a source chamber. A dielectric RF window separates the interior of the source chamber from the RF coil, in some cases, at atmospheric pressure. The power delivered to the RF coil can be adjusted to control the density of the plasma and the extracted ion beam current. Due to inherent weaknesses such as low fractionation of the monoatomic ion species, low power density and low temperature operation, RF ion sources face challenges.